Controlled thermal expansion of welds to enhance toughness

Abstract

A method is provided for forming a metallic overlay having enhanced toughness. The metallic overlay may be a weld, a metallic coating, or similar application. The method includes applying a glass forming metallic alloy to a substrate while the alloy is in a molten or semi-molten state. At the interface of the metallic alloy overlay and the substrate the substrate metal becomes at least partially molten and combines with the alloy to form metallurgical bonds. When the metallic alloy cools it experiences a high relative degree of thermal contraction. The metallurgical bonds between the substrate and the alloy constrain the contraction of the alloy at the interface with the substrate. This results in the inducement of compressive stresses in the metallic alloy overlay. The induced compressive stresses inhibit the formation of cracks in the overlay and / or mitigation of the effects of any cracks in the overlay.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Application No. 60 / 459,341 filed Apr. 1, 2003.FIELD OF THE INVENTION[0002]The present invention is directed at a toughening mechanism for improving the properties and performance of weld-type overlays. The toughness of the weld-type overlay is improved by controlling the thermal contraction of the weld overlay during cooling. The increased toughness weld-type overlays of the present invention may be utilized in many application including hardfacing, wear / overlay plate, as well as the rebuild and repair of metal parts.BACKGROUND OF THE INVENTION[0003]Often with conventional materials, there is an inverse relationship between hardness and toughness. Generally, as the hardness of the material increases there will be a corresponding, though not necessarily proportional, decrease in the toughness of the material. On reason for this inverse relationship is because the mechanism of dislocation...

AI Technical Summary

Benefits of technology

[0006]In a first embodiment the present invention is directed at a method for forming a metallic overlay comprising supplying a metal substrate with a thermal expansion coefficient “X”, supplying a metal alloy which has a thermal expansion coefficient “Y”, wherein Y>X, melting said metal alloy and applying said metallic alloy to said metal substrate to form an alloy / substrate interface, forming metallurgical bonds between said metallic alloy and said substrate at said alloy / substrate interface, and causing said alloy to shrink while said alloy is constrained at said alloy / substrate interface thereby developing a residual compressive stress in said metallic alloy.

[0007]In a second embodiment the present invention is directed at a method for forming a metallic overlay comprising supplying a metal substrate with a thermal expansion coefficient “X”, supplying a metal alloy which has a thermal expansion coefficient “Y”, wherein Y>X and wherein said metal alloy has a yield strength “Z”, melting said metal alloy and applying said metallic alloy to said metal substrate to form an alloy / substrate interface, forming metallurgical bonds between said metallic alloy and said substrate at said alloy / substrate interface, and causing said alloy to shrink while said alloy is constrained at said alloy / substrate interface thereby developing a residual compressive stress in said metallic alloy, wherein said compressive stress does not exceed the yield strength “Z”.

[0008]In a third embodiment the present invention is directed at a method for forming a metallic overlay comprising supplying a metal substrate with a thermal expansion coefficient “X”, supplying a metal alloy which has a thermal expansion coefficient “Y”, wherein Y>X and wherein said metal alloy has a yield strength “Z”, melting said metal alloy and applying said metallic alloy to said metal substrate to form an alloy / substrate interface, forming metallurgical bonds between said metallic alloy and said substrate at said alloy / substrate interface, and causing said alloy to shrink while said alloy is constrained at said alloy / substrate interface thereby developing a residual compressive stress in said metallic alloy, wherein said compressive stress does not exceed the yield strength “Z” and wherein said metal alloy has a hardness of greater than about 850 kg / mm2.

[0009]In yet another embodiment the present invention is directed at a method for forming a metallic overlay comprising supplying a metal substrate, supplying a metal alloy, melting said metal alloy and applying said metallic alloy to said metal substrate to form an alloy / substrate interface, forming metallurgical bonds between said metallic alloy and said substrate at said alloy / substrate interface, causing said alloy to cool to provide said alloy with a fracture toughness greater than 200 MPa m1 / 2 and a hardness greater than 5 GPa.

Problems solved by technology

When defects are introduced into a material, the defects may tie-up dislocations, thereby preventing the material from yielding.

While the thermal spray coatings industry is a mature industry and the application of a high performance coatings have long been used to dramatically improve the lifetime of a part, there are many military and industrial applications for which a thermal spray coatings approach is not sufficient to solve wear problems.

Problematic applications often involve heavy loads, high stress point loads, heavy impact, and gouging abrasion of the coated part.

Additionally, while thermal spray may be used for limited cases in the rebuild and repair of parts, weld on techniques will generally be necessary.

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